The present invention relates to head-up display (referred to as xe2x80x9cHUDxe2x80x9d in the following) devices for a vehicle. More specifically, this invention relates to a HUD device with reduced double-images. The present invention also relates to a laminated glass used for the windshield glass in such a HUD device.
In recent years, HUD devices have come into use not only in aircraft but also in land vehicles such as automobiles. HUD devices project information light signals emitted from information projecting means such as an LCD device onto the windshield glass, where it is reflected to provide the operator with necessary information. When HUD devices are used, the operator can allow an information display as a virtual image to enter his visual field beyond the windshield glass, so that he can perceive the information display without diverting his attention much from navigation.
Conventionally, information displays with a HUD device posed the problem of so-called ghost images. Ghost images appear when the information light signals reflected by the external surface of the windshield glass and the information light signals reflected by the internal surface of the windshield glass form virtual images at different positions. In a conventional windshield glass 101 illustrated in FIG. 20, light rays traveling from a light source 102 to the eyepoint of an observer 103 take two different light paths. In other words, a light path 124 taken by a light ray 121 that is reflected at an internal surface 111 does not match a light path 123 taken by a light ray 122 that is reflected at an external surface 112, so that virtual images 104 and 105 are formed at separate positions to cause ghost images (double-images).
In order to prevent ghost images from appearing, a windshield glass with a wedge-shaped cross section has been proposed.
For example, in JP3-209210A, two glass sheets with a polyvinyl butyral (PVB), film as an intermediate layer, which has been formed by extrusion so that its cross section is wedge-shaped, are attached to one another to form a laminated glass sheet. This laminated glass sheet is used for the windshield glass of a HUD device. The same publication teaches that due to the nonparallel internal and external surfaces of the windshield glass, the light path difference of the information light signals reflected at both surfaces can be decreased, and the image separation (double-image) caused by the light path difference can be reduced.
JP7-175007A teaches that in a HUD display device, ghost images can be reduced by configuring an intermediate layer or a glass sheet as a tapered sheet. The HUD device actually disclosed in this publication, as in JP3-209210A, uses a laminated glass sheet with a tapered intermediate layer.
JP7-195959A, like JP7-175007A, teaches that ghost images in a HUD device can be reduced by devising an intermediate layer or a glass sheet as a tapered sheet. Moreover, in the same publication, a HUD device using a windshield glass with a partially wedge-shaped cross section is disclosed. In this windshield glass, only the area portion in front of the operator is partially wedge-shaped. For such a windshield glass, this publication discloses in particular a laminated glass of glass sheets attached to each other with an intermediate layer that has been partially processed into a wedge shape by extending differentially. Moreover, this publication proposes a glass sheet that is tapered at a selected area portion, which is formed by adding a partially tapered glass piece to the glass sheet of a certain thickness, or partially polishing the glass sheet.
In addition, JP63-72122U discloses a front glass with a partially ground internal surface. As shown in FIG. 21, the surface of a windshield glass 131 in this publication is ground so as to form a reflecting surface 135 and a ground surface 136 that is connected to the reflecting surface 135. In this way, a light path 137 travelling from a light source 132 to an eyepoint 133 is unified. Also, a combiner 138 is formed on the reflecting surface 135.
As described above, the first method for suppression of ghost images in conventional HUD devices involves the processing of an intermediate layer, which joins two glass sheets, into a wedge shape. However, when an intermediate layer with such a wedge-shaped cross section is used, the problem arose that it became difficult to vent the air between the glass sheets and the intermediate layer in the process of joining the two glass sheets by means of the intermediate layer. Moreover, when producing small lots of intermediate layers that conventionally have been produced in large quantities, the manufacturing costs also rose.
The second method for suppression of ghost images involves the grinding of the surface of a glass sheet partially into a wedge shape. This method is described in detail in JP63-72122U. However, as described in this publication, the problem with this method is that the grinding of the glass surface (See FIG. 21) degrades the quality of the windshield glass due to the optical distortion caused by the refraction of light at the glass surface, and particularly by the refraction of light at an inflection point 140 at the glass surface.
Moreover, in recent years, screens of HUD devices have tended to become larger in accordance with the diversification of information to be provided. If the screen becomes larger, the reflecting surface of the glass surface also needs to be enlarged. When the reflecting surface is enlarged to a bigger size, incident angles of light from a light source cannot always be regarded as identical at some regions of the reflecting surface. However, in the conventional windshield glass described above, incident angles of light are regarded as the same within the reflecting surface, and the cases in which incident angles are different are not taken into consideration.
The present invention has been conceived in consideration of these circumstances, and one of its objects is to provide a HUD device with reduced ghost images and reduced optical distortion of the windshield glass without forming a wedge-shaped intermediate layer. It is another object of the present invention to provide a HUD device that can suppress ghost images effectively even in the case where the reflecting surface of a glass surface is enlarged. It is a further object of the present invention to provide a laminated glass used for the windshield glass of such a HUD device.
A first head-up display device according to the present invention comprises information projection means emitting information in the form of light rays, and a windshield glass having a reflecting surface for reflecting the light rays toward an observer inside a vehicle. In this device, a first light path is defined between a first reflecting surface prepared on an internal surface of the windshield glass and the observer by a first light ray that is emitted from the information projection means, reflected by the first reflecting surface, and projected toward the observer, and a second light path is defined between the internal surface and the observer by a second light ray that is emitted from the information projection means, refracted into the windshield glass at the internal surface, reflected by a second reflecting surface prepared on an external surface of the windshield glass, and refracted out of the windshield glass at the internal surface toward the observer.
The first reflecting surface and the second reflecting surface are non-parallel to each other so that the first light path and the second light path are approximating each other (preferably substantially matching each other) more than when the first reflecting surface and the second reflecting surface are arranged in parallel to each other. At least one surface selected from the first reflecting surface and the second reflecting surface is a ground reflecting surface formed by grinding the surface of the windshield glass so as to set the non-parallelity of the reflecting surfaces. The surface of the windshield glass includes a ground surface contacting the ground reflecting surface with an angle between 150xc2x0 and 210xc2x0, which is a difference of less than 30xc2x0 with 180xc2x0.
When the surface of a glass sheet is partially ground to form a reflecting surface that is not parallel to the other reflecting surface, light is refracted locally at an edge of the reflecting surface, so that optical distortion occurs in the windshield glass. Therefore, the above first HUD device is provided with a ground surface contacting a reflecting surface, which is formed so as to reduce this optical distortion.
Thus, in the first HUD device according to the present invention, ghost images can be suppressed effectively without processing an intermediate layer into a wedge shape, and optical distortion occurring when a glass sheet is partially processed can be suppressed.
Furthermore, a second head-up display device of the present invention is identical with the first HUD device in that at least one surface selected from the first reflecting surface and the second reflecting surface is a ground reflecting surface formed by grinding the surface of the windshield glass so as to set the non-parallelity of the reflecting surfaces. In addition to this aspect, the second HUD device of the present invention is characterized in that the ground reflecting surface has a distribution of angles with the surface of the windshield glass in a non-ground state so as to reduce the divergence between the first light path and the second light path caused by different incident angles of light rays from the information projection means in compliance with the position in the reflecting surface.
When images are enlarged in accordance with the diversification of information to be provided, the reflecting surface of the windshield glass is also enlarged. As the reflecting surface becomes larger, the reflecting surface having a constant angle with the non-ground surface cannot suppress ghost images effectively. Therefore, the above second HUD device is configured such that the angle between the ground reflecting surface and the non-ground surface is adjusted in compliance with the position in the reflecting surface.
Thus, since the above second HUD device is provided with a ground reflecting surface having a distribution of angles which is adjusted in this manner, ghost images can be suppressed more effectively than when a ground reflecting surface having a constant angle is used. The above HUD device is particularly effective in the case where images provided by the HUD device are large. In addition, the above HUD device can suppress ghost images without processing an intermediate layer into a wedge shape.